This invention relates to microfluidic apparatus for reading, writing and sorting magnetic tags attached to chemical and biological molecules and other entities. We describe apparatus for separating chemical or biological molecules or moieties each individually attached to a MBM tag miniature multi-bit magnetic tag capable of adopting a plurality of remanent magnetic configurations corresponding to binary information, the apparatus comprising: at least one input for said tagged molecules or moieties; at least two outputs for said tagged molecules or moieties; a microfluidic flow channel incorporating: magnetic readers to read said binary information; magnetic writers to write said binary information; and a switch to direct said tagged molecules or moieties to a selected said output responsive to said binary information.
